Highly regio- and stereoselective hydrosilylation of internal thioalkynes under mild conditions

A general and mild hydrosilylation of thioalkynes is described. With the cationic catalyst [Cp Ru(MeCN)₃]⁺ and the bulky silane (TMSO)₃SiH, a range of thioalkynes underwent smooth hydrosilylation at room temperature with excellent α regioselectivity and syn stereoselectivity. DFT calculations provided important insight into the mechanism, particularly the unusual syn selectivity with the [Cp Ru(MeCN)₃]⁺ catalyst. The sulfenyl group in the substrates was found to provide important chelation stabilization to direct the reaction through a new mechanistic pathway. A rich source of vinyl silanes: A general, mild, and highly stereoselective hydrosilylation of electron-rich alkynes gave a range of stereodefined multisubstituted vinyl silanes with high efficiency (see scheme; R¹, R²=alkyl, aryl; TMS=trimethylsilyl). Unprecedented syn selectivity was observed with the cationic catalyst [Cp Ru(MeCN)₃]⁺. DFT calculations provided important insight into the mechanism.